The present invention relates generally to valves, and more particularly to electromagnetically actuated valves for use with viscous clutches.
Viscous clutches are used in a wide variety of applications, for example as fan drives in automotive applications. The clutch employs silicone oil for the transmission of torque between two rotating components. It is possible to engage or disengage the clutch by allowing the oil into and out of the working area of the clutch. A valve is used to control the flow of the oil between the input rotor and the output housing. Recent designs have been employed that allow the oil to be stored in the rotating input portion of the clutch while the clutch is disengaged in order to keep the kinetic energy available to allow rapid engagement of the clutch from the off condition. This also allows the clutch to have very low output fan speed while in the off position. It has also become common for the clutch to be controlled electrically (i.e., electromagnetically). This has been done to increase the controllability of the clutch and to also have the clutch capable of responding to multiple cooling needs. Some of the possible cooling needs are coolant temperature, intake air temperature, air conditioning pressure, and oil temperature.
However, tolerances for known viscous clutch valves can be problematic, such as with respect to the flatness of valve components that provide a fluidic seal. For example, known valve assemblies utilizing a single-pivot valve lever that is not sufficiently flat can fail to provide a good seal to prevent viscous fluid from flowing out of a reservoir into the working area. Moreover, known electromagnetically controlled valve assemblies may require a relatively large magnetic field for actuation (i.e., overcoming a default spring biasing force), which can require an undesirably large electromagnetic coil. Large electromagnetic coils tend to be relatively heavy, expensive and power-intensive.
Thus, an alternative viscous clutch and associated valve assembly is desired.